Various semiconducting, photoactive and insulating materials have been investigated using XPS where the data is collected in a dynamic mode. This is achieved by recording the spectrum while applying an electrical signal in the form of ± 5 or 10 V d.c. bias, and/or square-wave pulses, without and under photoillumination using different lasers. This method enables us to probe and sort out the effects and contributions of the three fundamental processes operating; Charging, Photovoltage-Development, and Photoconductivity in a chemically specific fashion. Accordingly, the chemical shift differences between the n- and p-doped semiconductors are amplified due to the effect of the photovaltage operating in the opposite directions. Time and/or frequency dependence of various processes adds a new dimension to XPS for sorting out the effects of external stimuli (electrons, ions, photons, etc.) as well as the chemical nature of the material under investigation. Experimental results and various applications will be presented and discussed.